1. Field of the Invention
This invention relates in general to offshore drilling, and in particular to equipment and methods for providing electrical communication between a surface drilling platform or an ROV using an umbilical.
2. Prior Art
Control of subsea equipment is typically effected from the surface mounted control station via an umbilical. The umbilical typically carries hydraulic power and may include electrical power, and communication for control and monitoring of equipment in or on the well. When completing a subsea well for subsea production, a riser extends from a surface vessel and attaches to the subsea well. A tubing hanger is lowered on a conduit (typically termed a landing string) through the riser and landed in the tubing spool or wellhead assembly. A tubing hanger running tool, which is connected to the upper end of the tubing hanger sets the seal and locking member of landing of the tubing hanger in the wellhead or similar apparatus. The umbilical extends from the running tool alongside the conduit inside the riser to the surface platform. A lower marine riser package (“LMRP”) and subsea blowout preventer (“BOP”) are typically utilized for safety and pressure control. In arrangements in which the BOP provides the main basis for pressure control, the BOP typically closes in on and engages the outer surface of the landing string at a location above the tubing hanger running tool.
With a conventional subsea BOP rams may close or shear on the running tool at a point below the attachment of the umbilical to the landing string. BOP rams cannot seal around a conduit if the umbilical is alongside without damaging the umbilical, so the umbilical is terminated and the individual function lines to the tubing hanger running tool are ported through a “BOP spanner joint” that enables space out of the landing string and thereby enables closure of the BOP rams without damage to the control functions. This arrangement presents an obstacle to the use of a surface BOP for subsea completion operations as the spanner joint must be located at the surface location, resulting in a variable height depending on water depth that the umbilical must accommodate. Generally, also there is an inherent risk of damage to the umbilical during running and operation when used within subsea drilling risers. For this reason, a means of providing power and control external to the drilling riser system is attractive